N-long-chain acyl acidic amino acids, for example, an N-long-chain acyl glutamic acid, N-long-chain acyl aspartic acid or salts thereof such as sodium salts, potassium salts, triethanolamine salts and the like have been used as various agents such as detergents, dispersing agents, emulsifying agents, antibacterial agents and the like because they have surface activating action, sterilizing action and the like. N-long-chain acyl acidic amino acids or salts thereof are less irritating to the skin and the hair, and have therefore found wide acceptance in detergent compositions such as hair shampoos, body shampoos and the like.
As a method of forming an N-long-chain acyl acidic amino acid, for example, an N-long-chain acyl glutamic acid, a method is known in which glutamic acid is condensed with a long chain fatty acid halide in a solvent of water in the presence of an alkali (e.g., see Reference Example at the beginning of column 7 in Japanese Patent Publication No. 35,058/1973). However, this prior art method is not said to be a method which can satisfactorily be used industrially because of the low yield.
As a method of producing an N-long-chain acyl acidic amino acid in a high yield, a method is known in which the reaction is conducted in a solvent of water using a tertiary amine or a quaternary ammonium salt as a catalyst (Japanese Patent Publication No. 35,058/1973). However, because these catalysts may irritate skin, eyes, mucous membranes, etc. and also produce an unpleasant odor, a procedure and equipment for removing these catalysts remaining in the desired product are required. Thus, this method is not said to be an industrially satisfactory method.
As another method to increase the yield, a method is known in which a mixed solvent comprised of an organic solvent such as acetone, methyl ethyl ketone, dioxane, tetrahydrofuran or the like and water is used as a reaction solvent (Japanese Patent Publication No. 8,685/1979). However, the use of organic solvents poses health and safety hazards and requires special equipment in order to meet health and safety regulations which in turn causes extra operating costs to be incurred. Therefore, in view of the health and safety related issues, skin irritation, and odor associated with the use of organic solvents, equipment for removing them from the final product is required.
Likewise, a method is known in which a hydrous lower alcohol is used as a reaction solvent to increase the yield (Japanese Patent Publication No. 38,681/1976). However, this method also yields a product which has an undesirable odor due to the lower alcohol remaining in the final product, and a procedure for removing the same is required.